Sensitivity control for radio receiving systems



Dec. 18, 1934.-

SENSITIVITY CONTROL FOR RADIO RECEIVING SYSTEMS I I I I I 14 l l l l l 9 EM-iii H. J. J. M. DE R. DE BELLESCIZE Filed April 15, 1929 2 Sheets-Sheet l' INVENTOR HERRI J.J. M De R. m BELLESCIIE ATTORNEY Dec. 18, 1 3 H. J. J. M DE R. DE BELLESCIZE 1,934,400

SENSITIVITY CONTROL FOR RADIO RECEIVING SYSTEMS Filed April 15, 1929 2 Sheets-Sheet 2 INVENTOR KERR! J.J.M.De R.D ELLESCIZE BY 7% ATTORNEY Patented Dec. 18, 19 34 p UNITED STATES I 1,984,400 SENSITIVITY CONTROL FOR RADIO" T RECEIVING SYSTEMS I HenriJea'n. Joseph Marie de Regnauld de Bellescize, Paris," France; assignor toRadio Corpora-. tion of America, New York, N. Y., a. corporation of Delaware Application April 15, 1929, Serial No. 355,083* In France April 26, 1928 4 Claims. (01. 250-20) French Patent No..560,208, discloses a receiving arrangement in which the variations of potential set up by the detected current in a resistance connected abovejthe detector are fed to the grids of one or more tubes connected below the detector.

The result is that these variations of potential modify the sensitiveness of the receiver in inverse sense compared with the strength of the incoming oscillations.

The objects of this invention will be apparent from the following detailed description when read in connection with the appended drawings in which l Figure 1 illustrates diagrammatically a device for lessening the effect of static;

Figure 2 shows a circuit adapted to correct so called fading disturbances;

Figure 3 illustrates another modification of the invention shown in Fig. 2.

The arrangement as shown in Figure 1 comprises one or more tuned circuits1-4 excited by the oscillations coming in at 0 in'the antenna, an amplifier 8 which mayor may not be utilized, and detecting means consisting of tube 9. The detected current in the scheme shown in Fig. 1 sets up in the assembly comprising the resistance and condenser 10-11 a potential proportionalto the intensity of the oscillations picked up by the antenna. As arranged an increase of potential when applied to the grids of tubes 40-41tends to more or less diminish the resistance of the filament-plate'circuit of tubes 40-41 while shunting the circuits 1 and 4. "As a result of the decrease in damping of the circuits, there occurs a reduction in-the sensitivity of the receiver. The slide contact 45 is regulated in such a way that the plate circuits of the tubes 40-41 furnish energy, only under the action of stray oscillations more powerful than the signal. It will be evident that if'for some reason or another, the strength of the signal should exceed the predetermined value, the sensitivity of the receiver would fall off automatically and would bring back or restore the detected currentto an invariable value. The audio frequency part of the receiver comprising direct current amplifier stages 14-19-24 is as described in the first addition No. 26,608 of the above-mentioned patent. 26 denotes the reading or recording apparatus. The slide contact controlling tubes 40 and 41 may be connected to any one of the battery leads 12-17-22, provided that the direction of the corresponding plate currents was suitable. The ensuing result would also have been the same if circuits 1-4, instead of being coupled directly, had been coupled by way of tubes.

Hence, the arrangement illustrated in Figure 1 was originally used for the reduction of stray oscillations more powerful than the signal.

The present invention provides a newapplication of arrangements of this kind for a rough correction of the changes in amplitude caused by what is known as fading. This can be done in a simple way by changin the regulation in a suitable manner. In this way, the device canbe actuatedby the signal itself so that the sensitivity of the receiverivariesinversely as the latter.

' This novel application of the scheme is more efliciently realized by the circuit arrangements shown in Figures 2 and 3 wherein, for the sake of greater clearness, the same receiver apparatus has been retained, but it will be understood that the invention isapplicable to any kind of receiver furnishing a sufficiently strong rectified current.

The chief change required by the new application consists in increasing the time constantto a large degree in the resistance capacity circuit (10-11 in Figures 2and 3) intended to control and regulate the sensitivity of the stages or stage as the case may be below the detector. This time constant should be rather high in order that the alterations in the amplitude of the signal forming the communication proper (modulation of 'o f'whi ch the sensitivity of 5 the receiver varying inversely asthe amplitude constituting the signal, the latter would tend to vanish. With this reservation, the invention is applicable to any mode of keying or modulation. In telegraphy the succession of dots and dashes results in an accumulation of a charge in condenser 11, therefore the condenser will have to be much larger. Thus the slower the keying the larger the condensers (11a, 11b, so that the signal will occasion across the resistance, 10 a, permanent potential variation undergoing but negligible variations.

Referring to Figure 2 it will be seen that substantially the same elements are there shown as in Figure 1. However, because of the present novel application, circuit 10-11 as well as contact slide 45 have been arranged at the end of the receiver where the amplitude is higher so as to produce a more powerful action upon tubes 40-41. The part of source 12 that is employed is chosen in such a way that, in the absence of a signal the potential of grids 40-41 is more negative than the value neutralizing the corresponding plate currents. This oifers the two-fold advantage of insuring for the receiver its maximum sensitivity in the presence of feeble signals and of increasing in relative value the rate of desensitizing under the action of strong signals. The resistance capacity circuit and 11a 11b, 11c) is along the lines as before indicated.

The scheme shown in Figure 3 is identical with the preceding one except that tube 46 Whose plate potential variations act upon the system 4041 is connected in parallel in relation to the reception properly so called. The operation is exactly the same.

More specifically the circuit of Figure 3 shows an extra tube 46 connected in parallel with tube 19. It is evident from the drawings that whatever changes in potential are impressed on the grid of the tube 19 will necessarily be impressed 'on the grid of tube 46 so that in reality these changes through the arrangements 10, 11 etc. 'Will aifect tubes 40 and 41 as desired. No difference in operation results from the arrangement ing circuit, an audio frequency amplifying means,

a resistance and a capacity circuit forming a parallel circuit having a relatively high time constant connected in the output of said audio frequency amplifying means, the time constant of said parallel circuit acting to substantially elimi nate the energy in said'parallel circuit from the fluctuations of the energy received due 'to'the signals, means controlled by thedetected current for setting up variations of potential across said resistance and a plurality of triodes having their outputs connected to the inputs of'said radio frequency stages to shunt said latter and having 1 their grids subjectedto potential variations created across said resistance said triodes being adapted to modify the sensitiveness of the'said circuits of radio frequency amplification in accordance with the variations of potential in the said resistance.

2. In a receiver apparatus, means for automatically varying the sensitivity of an amplifier stage preceding the detector inversely to the level of the energy received comprising the circuit of a controlled electrode connected in parallel in said stage, the resistance of this controlled circuit depending upon another electrode polarized by a second circuit traversed by the detected current and having a high time constant chosen so as to "subtract the energy of said second circuit from the fluctuations of the energy received due to the signals, the resistance of the circuit of the controlled electrode remaining infinite as long as the detected "current falls below a predetermined value.

3. In a receiver for receiving modulated signal energy, a radio frequency amplifier stage, a detectors'tag'e and an audio frequency circuit where- 'by incoming signal energy is amplified in said radio frequency amplifier stage, detected in said detector and the detected energy amplified in said audio frequency circuit, said audio frequency circuit having a time constant larger than the periods of modulation of the signal energy, means for automatically controlling the sensitivity of said radio frequency amplifier stage comprising a variable resistance in parallel With said radio frequency stage said variable resistance comprising a space'discharge device having its resistance controlled by the potential drop set up bythe detached signal currents in the output of the said audio frequency circuit.

4. In a receiving circuit provided with a stage of radio frequency amplification, a detecting 'circuit and an audio frequency amplifier, a parallel arrangement, comprising a resistance and a capacity circuit having a relatively high time constant connected in the output of said audio frequency amplifier, the time constant of said parallel circuit acting to substantially eliminate current fluctuations therein caused by signal modulations of the received signalling energy, the detected current flowing through said resistance being adapted to set up potential variations across said resistance and a space current path connected across the input of said stage ofradio frequency amplification arranged so'that said path shunts said input circuit and means controlled by the :potential variations created across said resistance to modify the resistance characteristics of said path in accordancewith the variations of potential across said resistance so as to change the sensitivity of said stage of-radio frequency amplification.

HENRI JEAN JOSEPH MARIE DE REGNAULD DE BELLESCIZE. 

